I wondering what is the general consensus on CNCzone about using delrin, or maybe even PTFE, as a linear bearing? I need to get ordering parts in as early as possible as my gantry router will be my final shop project for grade 10.

PerT used plastic delrin bearings, and it seems to be a well made machine so I'm wondering would I be able to get away with using it as a linear bearing, without much play and still be relatively easy to push?

(Close up of PerT's bearing set-up) (http://www.cnczone.com/gallery/data/505/6760CNC2.jpg)

It will be pretty much a 2" cube of delrin or PTFE-delrin(Delrin AF?) that will be drilled with 4 mounting holes and a hole for the 1" drill rod bar I will be using. A block on each side of the bottom of the Y-Z assembly that will be bolted together with a spacer between the bearings, as PerT used. Silicon lubricant will work its way in there too.

As I'm getting rather short on time, the ease of attaching delrin cube to the Y-Z axis assembly is much more attractive then the much used angle iron design.

Adjustability may turn out to be on the hard side, but I will buy two feet of the stuff as it is not too expensive.

As for accuracy of the cuts, I do have access to proper CNC mills and routers, lathes, etc at my school.

Therefore, barring any inaccuracy in the cuts of the bearings and in the drill rod bar it will slide on, what can I expect in terms of usability, play, and friction?

Thank you,
Evan Crawford

Delrin can expand and contract a lot with temperature changes. As it warms up from friction, it will get looser.

How much so? The most accurate I really want this is for 0.5mm pitch microcontroller pcbs. The rest of my work will do quite fine with larger tolerances. Also I have decided on Teflon-filled delrin (AF), will it still slide fairly easily? I'm short on time, and if it slides easily, its my top option.

I'm looking at a Delrin physical properties sheet.
Coefficient of thermal expansion degree F 0.000068 this is inch per inch per degreee F. 10 degree F increase on a 1 inch part would grow 0.00068
Carl

There is a whole range of plastics designed for just this purpose. Many have a lubricating agent built in. I have used both teflon and Delrin which is my preference because it is easier to machine to a precise bore. Holes really need to be bored out on the lathe or mill, drilling is just for the first rough cut. Your boring tool will need to be ultra sharp and set exactly on the centre height or a micro poofteenth below centre otherwise it will dig in. If you have trouble getting the correct bore, bore out as close as possible or just oversize then slit the block half way thru. It may close up, not a problem as you have left room for three screws in line passing thru the slit into the opposite side of the block. One is threaded into the near side to open up the hole, the other two threaded into the far side to pull the hole in. Hope this is clear.

There is a whole range of plastics designed for just this purpose. Many have a lubricating agent built in. I have used both teflon and Delrin which is my preference because it is easier to machine to a precise bore. Holes really need to be bored out on the lathe or mill, drilling is just for the first rough cut. Your boring tool will need to be ultra sharp and set exactly on the centre height or a micro poofteenth below centre otherwise it will dig in. If you have trouble getting the correct bore, bore out as close as possible or just oversize then slit the block half way thru. It may close up, not a problem as you have left room for three screws in line passing thru the slit into the opposite side of the block. One is threaded into the near side to open up the hole, the other two threaded into the far side to pull the hole in. Hope this is clear.

Hi - do you have a link to plastic like you describe with self lubricating? Thanks

A very useful Australian website for plastics information which also provides links into the international scene is:
www.cuttosize.com.au
For those who found the term "micropoofteenth" a little confusing it is essentially an imperial measurement with a metric crossover, however it takes many years of fiddling about in the shed to reach an imprecise definition of the term.